Influence of cationic porphyrins on melting parameters of calf thymus DNA

The influence of water soluble cationic $3N$- and $4N$-pyridyl porphyrins with different peripheral substituents on melting parameters of Calf Thymus DNA has been studied. It was shown, that the presence of porphyrin changes the shape and parameters of DNA melting curve. The decrease of $\Delta T$ in the presence of $3N$-porphyrins is observed. Because of the intercalation binding mechanism occurs in $GC$-rich regions of DNA, which is the reason for the decrease melting interval. While even at the low relative concentration for $4N$-porphyrins already the external binding mechanism "turns on” and as a result the change in the melting parameters of DNA upon complexation with these porphyrins is not observed.